Such a so-called relief-port master cylinder is disclosed, for example, by DE 19 28 849 A1, which is incorporated by reference. The two pistons of the master cylinder have axial compensating bores through which, when the brake actuation is released, fluid is drawn from the refill chamber in the direction of the pressure chamber. For this purpose a sealing lip of the cup seal is pressed inward, so that the fluid can flow over the sealing lip. A filling plate, which protects the cup seal from damage, is furthermore arranged between the piston and the cup seal. The filling plate tilts inward with the cup seal and fluid likewise flows over it when the brake actuation is released.